This invention relates to a diamond-like carbon (DLC) coating provided on (directly or indirectly) a glass or other substrate. More particularly, in certain preferred embodiments, this invention relates to a highly tetrahedral amorphous diamond like carbon coating on a soda inclusive glass substrate (e.g. on a soda lime silica glass substrate) for purposes of repelling water and/or reducing corrosion on the coated article. Ion beam and filtered carbon cathodic arc deposition are preferred methods of deposition for the coating.
Soda inclusive glasses are known in the art. For example, see U.S. Pat. No. 5,214,008, which is hereby incorporated herein by reference.
Soda lime silica glass, for example, is used for architectural glass, automotive windshields, and the like. The aforesaid ""008 patent discloses one type of soda lime silica glass known in the art.
Unfortunately, conventional soda inclusive glasses are susceptible to environmental corrosion which occurs when sodium (Na) diffuses from or leaves the glass interior. This sodium, upon reaching the surface of the glass, may react with water to produce visible stains or smears (e.g. stains of sodium hydroxide) on the glass surface. Such glasses are also susceptible to retaining water on their surfaces in many different environments, including when used as automotive windows (e.g. backlites, side windows, and/or windshields). These glasses are also susceptible to fogging on the interior surface thereof in automotive and other environments.
In view of the above, it is apparent that there exists a need in the art to prevent and/or minimize visible stains/corrosion on soda inclusive coated glass surfaces. There also exists a need in the art to provide a strong protective coating on window substrates. Other needs in the art include the need for a coating on glass that reduces the coated article""s susceptibility to fogging up in automotive and other environments, and the need for a coated glass article that can repel water and/or dirt.
It is known to provide diamond like carbon (DLC) coatings on glass. U.S. Pat. No. 5,637,353, for example, states that DLC may be applied on glass. The ""353 patent teaches that because there is a bonding problem between glass and that type of DLC, an intermediate layer is provided therebetween. Moreover the ""353 patent does not disclose or mention the highly tetrahedral amorphous type of DLC used in many embodiments set forth below. The DLC of the ""353 patent would not be an efficient corrosion minimizer on glass in many instances due to its low density (likely less than 2.0 gm/cm3). Still further, the DLC of the ""353 patent is deposited in a less than efficient manner for certain embodiments of this invention.
It is known that many glass substrates have small cracks defined in their surface. The stress needed to crack glass typically decreases with increasing exposure to water. When water enters such a crack, it causes interatomic bonds at the tip of the crack to rupture. This weakens glass. Water can accelerate the rate of crack growth more than a thousand times by attacking the structure of the glass at the root or tip of the crack. Strength of glass is in part controlled by the growth of cracks that penetrate the glass. Water, in these cracks, reacts with glass and causes it to crack more easily as described in xe2x80x9cThe Fracturing of Glass,xe2x80x9d by T. A. Michalske and Bruce C. Bunker, hereby incorporated herein by reference. Water molecules cause a concerted chemical reaction in which a silicon-oxygen bond (of the glass) at the crack tip and on oxygen-hydrogen bond in the water molecule are both cleaved, producing two silanol groups. The length of the crack thus increases by one bond rupture, thereby weakening the glass. Reaction with water lowers the energy needed to break the silicon-oxygen bonds by a factor of about 20, and so the bond-rupture allows glass cracks to grow faster.
Thus, there also exists a need in the art for preventing water from reaching silicon-oxygen bonds at tips of cracks in a glass substrate, so as to strengthen the glass.
It is a purpose of different embodiments of this invention to fulfill any or all of the above described needs in the art, and/or other needs which will become apparent to the skilled artisan once given the following disclosure.
An object of this invention is to provide a coated article that can shed water (e.g. automotive windshield, automotive backlite, automotive side window, architectural window, etc.).
Another object of this invention is to provide a system or means for reducing or minimizing corrosion on soda inclusive coated glass articles.
Another object of this invention is to provide a coated glass article wherein a DLC coating protects the glass from acids such as HF, nitric, and sodium hydroxide (the coating may be chemically inert).
Another object of this invention is to provide a coated glass article that is not readily susceptible to fogging up.
Another object is to provide a barrier layer with no pin holes on a glass substrate.
Another object of this invention is to provide a coated glass article that is abrasion resistant, and/or can repel dirt and the like.
Another object of this invention is to provide a glass substrate with a DLC coating inclusive of a highly tetrahedral dense amorphous carbon layer, either in direct or indirect contact with the substrate.
Another object of this invention is to provide a DLC coating on a substrate, wherein the coating includes different portions or layers with different densities and different sp3 carbon-carbon bond percentages. The ratio of sp3 to sp2 carbon-carbon bonds may be different in different layers or portions of the coating. Such a coating with varying compositions therein may be continuously formed by varying the ion energy used in the deposition process so that stresses in the coating are reduced in the interfacial portion/layer of the DLC coating immediately adjacent the underlying substrate. Thus, a DLC coating may have therein an interfacial layer with a given density and sp3 carbon-carbon bond percentage, and another layer with a higher density and higher sp3 carbon-carbon bond percentage.
Generally speaking, this invention fulfills certain of the above described needs/objects in the art by providing a coated glass comprising:
a glass substrate including at least about 5% by weight soda/Na2O;
an amorphous carbon layer provided on the glass substrate in order to reduce corrosion or stains on the coated glass, wherein said amorphous carbon layer includes sp2 and sp3 carbon-carbon bonds; and
wherein the amorphous carbon layer has more sp3 carbon-carbon bonds than sp2 carbon-carbon bonds.
In other embodiments, this invention fulfills certain of the above described needs in the art by providing a coated glass comprising:
a soda inclusive glass substrate comprising, on a weight basis, from about 60-80% SiO2, from about 10-20% Na2O, from about 0-16% CaO, from about 0-10% K2O, from about 0-10% MgO, and from about 0-5% Al2O3; and
a non-crystalline diamond-like carbon (DLC) coating provided on the glass substrate, wherein the DLC coating includes at least one highly tetrahedral amorphous carbon layer having at least about 35% sp3 carbon-carbon bonds.
In certain embodiments, the glass substrate is a soda lime silica float glass substrate.
In preferred embodiments, the entire DLC coating or alternatively only a layer within the DLC coating, has a density of from about 2.4 to 3.4 gm/cm3, most preferably from about 2.7 to 3.0 gm/cm3.
In certain embodiments, the tetrahedral amorphous carbon layer has the aforesaid density range and includes at least about 70% sp3 carbon-carbon bonds, and most preferably at least about 80% sp3 carbon-carbon bonds.
In certain embodiments, the DLC coating includes a top layer (e.g. from about 2 to 8 atomic layers, or less than about 20 xc3x85) that is less dense than other portions of the DLC coating, thereby providing a solid lubricant portion at the top surface of the DLC coating. Layered graphene connected carbon atoms are provided in this thin layer portion. The coefficient of friction is less than about 0.1 for this thin layer portion.
Another advantage of this invention is that the temperature of the glass substrate is less than about 200xc2x0 C., preferably less than about 150xc2x0 C., most preferably from about 60-80xc2x0 C., during the deposition of DLC material. This is to minimize graphitization during the deposition process.
This invention further fulfills the above described needs in the art by providing a window having a substrate and a highly tetrahedral amorphous carbon layer thereon, wherein the substrate is or includes at least one of borosilicate glass, soda lime silica glass, and plastic.
This invention will now be described with respect to certain embodiments thereof, along with reference to the accompanying illustrations.